Sarcoidosis is a multisystem disease characterized by granulomatous inflammation in affected organs. There are no useful biomarkers to confirm a diagnosis of sarcoidosis. A consensus among the medical community is that there is no blood test with sufficient specificity and sensitivity to be useful as a diagnostic test. Confirmation of a diagnosis of sarcoidosis in most cases requires a biopsy with its attendant risks and costs.
Using a proteomic approach, mKatG has been identified as a tissue antigen and target of the immune response in sarcoidosis (J. Exp. Med. (2005) 201:755-67; U.S. Pat. Appl. Pub. No. US 2009/0175798). An immunoassay was used to identify T cell responses to mKatG and this allowed the detection of a secreted cytokine, interferon-gamma (INFγ), in response to mKatG. However, this immunoassay, using INFγ-ELISPOT, lacked the ability to distinguish between individuals with sarcoidosis and individuals with tuberculosis (TB) infection from Mycobacterium tuberculosis with or without a positive purified protein derivative (PPD) skin test (also called a tuberculin skin test) or individuals previously vaccinated with BCG (Bacillus Calmette-Guérin), derived from an attenuated strain of Mycobacterium bovis. Both of those conditions gave positive reactions to the INFγ-ELISPOT assay (T cell responses to mKatG in 50% of sarcoidosis patients and 50-60% BCG+ or PPD+ subjects). (J. Immunol. (2008) 181:8784-96). In addition, this assay could not distinguish sarcoidosis from individuals with non-tuberculous mycobacterial infection. All of these ailments have disease manifestations that can mimic or overlap with manifestations of sarcoidosis, and thus, these ailments must be excluded before a diagnosis of sarcoidosis can be confirmed.
What is needed is a safer protocol with adequate specificity and sensitivity to assist clinicians in confirming a diagnosis of sarcoidosis.